In a vapor recovery fuel dispensing nozzle of the general type disclosed in U.S. Pat. No. 3,866,636, No. 4,143,689, No. 4,235,266 and No. 4,418,730, it is common to use a pressure responsive check valve in the fuel line or passage within the nozzle body adjacent the inner end of the fuel dispensing spout. The check valve opens when fuel is supplied through the manually actuated control valve within the nozzle body, and a venturi suction or bleed passage extends from the annular seat of the check valve to the outer end portion of the spout. The venturi passage also extends to a diaphragm actuated mechanism which automatically closes the manually actuated valve when the bleed passage is blocked by fuel at the outer end of the spout. This form of automatic fuel shutoff is also commonly used in conventional fuel dispensing nozzles without a vapor return passage for a vapor recovery system.
One of the problems encountered with a vapor recovery fuel dispensing system is the accumulation of liquid fuel within the vapor return passage of the flexible coaxial hoses as a result of condensation of fuel vapors within the passage and the splash back of fuel during use of the dispensing nozzle for refueling. If too much liquid fuel collects within the vapor return passage defined between the coaxial hoses, the vapor return passage becomes blocked, and the vapor recovery system no longer operates.
One system for removing accumulated liquid fuel within the vapor return passage defined between coaxial hoses, incorporates a venturi system as disclosed in U.S. Pat. No. 4,687,033. In this patent, the venturi system is located within a coupling which-connects the coaxial hoses to the dispensing nozzle and includes a flexible rubber tube which extends downwardly into the annular vapor return passage defined between the coaxial hoses and terminates with an inlet located at the lowest point of the drape in the flexible hoses. The venturi system aspirates the liquid fuel within the vapor passage into the fuel supply passage which extends into the dispensing nozzle. The patent also mentions that the venturi system could also be located within the dispensing nozzle. Liquid fuel accumulated within the vapor return passage defined between the coaxial hoses has also been aspirated into the fuel supply passage by a venturi system located within the coaxial hoses at the lower most point of the drape in the hoses, and this venturi system is produced by Dayco Products, Inc.
The addition of a venturi aspirating system or device within the coaxial hoses or between the coaxial hoses and the dispensing nozzle as disclosed in above-mentioned U.S. Pat. No. 4,687,033, produces an additional flow restriction and pressure drop within the fuel supply passage extending to the dispensing nozzle. The flow rate reduction as a result of the additional restriction is on the order of 20% to 40%. Furthermore, the further upstream the venturi or aspirating device is located within the coaxial hoses, the higher the differential pressure that is required across the venturi or aspirating device to produce the desired suction. In order to obtain a higher pressure differential, the venturi must be more restrictive, which results in decreasing the flow rate.
The above-mentioned aspirating devices will not function properly below a minimum fuel flow rate such as 4 to 6 gallons per minute. To prevent a back flow of fuel through the venturi device and into the vapor return passage when the fuel flow rate is low due to partially opening the manually actuated flow control valve, a check valve is required in the venturi device. This check valve presents an additional pressure drop for which the venturi device must produce an additional pressure differential to overcome, thus further reducing the efficiency of the venturi device.